Was just wondering about this bulb. I got this fixture from someone and one bulb needs to be replaced. Is the F18 the length of it? Also was wondering is this strong enough to have corals or would it just be better to have a FOWLR tank? The lights are for a 20 gallon tank that im trying to start. Thanks

Is the tank a 20 long (30") or 20 high (24")? Either way, it's probably a 24" bulb. If that's a 2 bulb fixture, you could do FOWLR. There are a few low light corals you could probably keep, like mushrooms, green star polyps, or button polyps.